Presented at the Neonatal Society 2015 Summer Meeting.
Shetty S, Bhat P, Peacock JL, Milner AD, Greenough A
Division of Asthma, Allergy and Lung Biology, MRC Centre for Allergic Mechanisms in Asthma, King’s College London
Background: During assist control ventilation (ACV), ventilator inflations are triggered by the onset of the infant’s respiratory efforts. In contrast, during proportional assist ventilation (PAV) ventilator pressure is servo controlled throughout each respiratory cycle. In addition, the ventilator can provide inflation pressure in phase with the tidal volume change in order to reduce the compliance load (elastic unloading) and in phase with the flow volume change to reduce the resistance load (resistive unloading). We have previously demonstrated in a one hour cross over period study PAV compared to ACV was associated with a significantly lower work of breathing and oxygenation index and higher respiratory muscle strength (1). We, therefore, hypothesized that PAV compared to ACV would result in a higher oxygenation index over a four hour period, the longest time PAV has been studied in vivo.
Methods: A randomised crossover study in prematurely born infants, ventilator dependent beyond the first week after birth was undertaken. Prior to the start of each study, the infant’s compliance was determined using the results from the Stephanie ventilator, which delivered both ACV and PAV. During PAV, 100% elastic unloading was used. At the end of each four hour period on ACV and PAV, the oxygenation index was calculated. The planned sample size was 18 infants to allow a detection between the two ventilator modes of a difference equivalent to 0.7 SD in the oxygenation index with 80% power and a two sided significance of 5%.
Results: Infants with a median gestational age 25 (range 24-33) weeks were studied at a median postnatal age of 19 (range 10-105) days. Their median baseline compliance was 0.4 (range 0.3-1.1) mls/cmH2O and resistance was 155 (range 66-252) cmH2O/l/sec. Recruitment was stopped at eight patients, as all their OI results were in favour of PAV (p=0.004). The median FiO2(p=0.049), the median mean airway pressure (p=0.012) and the median oxygenation index (p=0.012) were all lower on PAV.
Conclusion: These results suggest that PAV compared to ACV is advantageous for prematurely born infants with evolving or established BPD.
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1. Bhat, P., et al. Crossover study of proportional assist versus assist control ventilation. Arch Dis Child Fetal Neonatal Ed, 2015. 100(1): F35-F38.